The present invention relates to detergent compositions useful for dishwashing.
The invention also relates to a method of washing dishes using such detergent compositions and to specific secondary alkyl sulfates in combination with ether sulfates suitable for use in such detergent compositions.
The term "dishes" as used in the following description indicates utensils that maybe required to be washed free from food particles and other food residues, greases, proteins, starches, gums, dyes, oil, and burnt organic residues.
Liquid dishwashing compositions for use in manual dishwashing are well-known and have met with a high degree of acceptance by consumers primarily because of their good washing and foaming properties and convenient form for use.
Most of the formulations in commercial use at the present time are based on synthetic organic detergents that, together with supplementary materials often used, give them satisfactory detergency and foaming properties. Historically, the main synthetic organic detergent used in such compositions has been formed from alkyl benzene sulfonates. Research, however, continues in an effort to provide alternatives to alkyl benzene sulfonates that are more environmentally acceptable. One such solution has been the development of secondary alkyl sulfates. Secondary alkyl sulfates are generally prepared from straight chain C.sub.10 -C.sub.18 alpha olefins or internal olefins and, depending on the reaction conditions during sulfonation, it is possible to produce C.sub.10 -C.sub.18 secondary alkyl sulfates having the sulfate group predominantly in the 2- or 3-position of the alkyl chain, or C.sub.10 -C.sub.18 secondary alkyl sulfates having the sulfate group more randomly distributed on the alkyl chain. During such preparation, the secondary alkyl sulfates produced have a mixture of carbon chain lengths.
As noted in U.S. Pat. No. 4,235,752, however, the performance of such secondary alkyl sulfates is poor compared to the wellknown alkyl benzene sulfonates. U.S. Pat. No. 4,235,752 therefore teaches that a small group of secondary alkyl sulfate "isomers" are particularly useful in detergent compositions. In particular, the C.sub.14.sup.-2, C.sub.15.sup.-2/3/4/5/6, C.sub.16.sup.-3/4/5/6/7, and C.sub.17.sup.-7/8/9 secondary alkyl sulfates are described as being useful where the suffix number indicates the carbon atom number on the alkyl chain on which the sulfate group is attached.
A particular problem with generally available detergents exists when the water used for washing is soft (i.e., has a hardness level less than 25 ppm as CaCO.sub.3). As used in the following specification and claims, the hardness level is expressed in ppm as CaCO.sub.3. At these low water hardness levels, the stability of the foam can be inadequate. Another problem with generally available detergents exists when the water used for washing has a hardness level greater than about 300 ppm (as CaCO.sub.3). At a high hardness level the amount of foam produced and the performance of the detergent is reduced. Consequently, a need exists for a dishwashing detergent that provides good foam stability over a wide range of water hardness levels.
Unexpectedly, it has been found that an improved dishwashing composition can be formulated by using a combination of specific secondary alkyl sulfates with an ether sulfate, where the secondary alkyl sulfate is selected from the group consisting of C.sub.14 or C.sub.16 secondary alkyl sulfates and their salts and where the secondary alkyl sulfate is substantially free from other carbon lengths. The combination, in a range of ratios of the specific secondary alkyl sulfate to the ether sulfate, provides improved washing performance over a range of water hardness levels as compared to what would be expected based on the performance of either the alkyl sulfate or the ether sulfate alone.